i.rectify: add test file

[jayneel-shah18]

This PR introduces a comprehensive regression test suite for the i.rectify module in GRASS. The tests cover the core rectification workflows, including affine and polynomial transformations, flag-specific behaviors, and region/resolution control.

Tests Included

• test_affine_rectification

  • Verifies a first-order (affine) polynomial transformation using cubic interpolation.
  • Ensures that spatial transformation and pixel values remain consistent with expected statistics.

• test_polynomial_order2_rectification

  • Validates 2nd-order polynomial transformation using linear interpolation.
  • Tests numerical stability and interpolation accuracy when extending beyond affine geometry.

• test_polynomial_order3_rectification

  • Verifies 3rd-order polynomial transformation with lanczos interpolation.
  • Demonstrates support for higher-order models and tests precision of the resampling algorithm.

• test_region_restriction

  • Tests the -c flag which restricts the output to the current computational region.
  • Confirms geographic extents of rectified rasters match the region bounds (via r.info).

• test_c_flag_with_resolution_override

  • Ensures that the -c flag takes precedence over the resolution= parameter.
  • Validates that output resolution aligns with the region and not the explicit input.

• test_automatic_rectification

  • Uses the -a flag to automatically rectify all maps in the group.
  • Confirms multi-raster handling and that results match expected statistical summaries.

• test_thin_plate_spline

  • Tests -t flag for thin plate spline (TPS) interpolation.
  • TPS is nonlinear and sensitive to control point configuration; this test validates the transformation correctness.

• test_resolution_parameter

  • Verifies the resolution= parameter sets the desired output resolution when -c is not used.
  • Ensures output maps honor the specified resolution and dimensions.

The suite validates correctness using raster inputs and univariate statistics on rectified outputs. Looking forward to feedback and improvements!

[petrasovaa]

For r.info you can use format=json:

Suggested change

	info = gs.parse_command("r.info", map="rectify_band1res2", flags="g")
	self.assertEqual(float(info["nsres"]), 2.0)
	self.assertEqual(float(info["ewres"]), 2.0)
	info = gs.parse_command("r.info", map="rectify_band1res2", format="json")
	self.assertEqual(info["nsres"], 2.0)
	self.assertEqual(info["ewres"], 2.0)